1. Field of the Invention
The present invention relates to a plasma display apparatus and driving method thereof.
2. Background of the Related Art
A plasma display panel (hereinafter, referred to as “PDP”) is adapted to display an image including characters or graphics by light-emitting phosphors by ultraviolet of 147 nm generating upon discharging of inert mixed gas such as He+Xe or Ne+Xe.
FIG. 1 is a perspective view illustrating the construction of a three-electrode AC surface discharge type PDP having a discharge cell structure arranged in the form of matrix in the prior art.
Referring to FIG. 1, the three-electrode AC surface discharge type PDP 100 includes a scan electrodes 11a and a sustain electrodes 12a formed on an upper substrate 10, and an address electrodes 22 formed on a lower substrate 20. Each of the scan electrodes 11a and the sustain electrodes 12a are composed of a transparent electrode, e.g., indium-tin-oxide (ITO). Metal bus electrodes 11b, 12b for reducing resistance are formed in the scan electrodes 11a and the sustain electrodes 12a, respectively. The upper substrate 10 on which the scan electrodes 11a and the sustain electrodes 12a are formed are stacked with an upper dielectric layer 13a and a protection film 14. The upper dielectric layer 13a is accumulated with wall charges generated upon plasma discharging. A protection film 14 serves to prevent damage of the upper dielectric layer 13a due to sputtering generating upon plasma discharging, and also to increase emission efficiency of secondary electrons. The protection film 14 is usually formed of oxide magnesium (MgO).
On the other hand, on the lower substrate 20 on which an address electrode 22 is formed is formed a lower dielectric layer 13b and barrier ribs 21. On the surface of the lower dielectric layer 13b and the barrier ribs 21 is coated with a phosphor layer 23. The address electrodes 22 is formed in a direction to cross the scan electrodes 11a and the sustain electrodes 12a. The barrier ribs 21 are formed parallel to the address electrodes 22, and serve to prevent ultraviolet and a visible ray generated by discharging from leaking toward neighboring discharge cells. The phosphor layer 23 is light-emitted by ultraviolet generated upon plasma discharging to generate one of red R), green (G) and blue (B) visible rays. An inert mixed gas for gas discharging, such as He+Xe or Ne+Xe, is injected into discharge spaces of the discharge cell, which are defined between the upper substrate 10 and the barrier ribs 21 and between the lower substrate 20 and the barrier ribs 21. A method of driving the conventional PDP constructed above will now be described with reference to FIG. 2.
FIG. 2 shows a driving waveform for explaining a method of driving the conventional PDP. Referring to FIG. 2, the conventional PDP is driven with it being divided into a reset period for initializing the whole screen, an address period for selecting a cell, and a sustain period for maintaining discharge of a selected cell.
First, the reset period is driven with it being divided into a set-up period SU and a set-down period SD. In the set-up period SU, a ramp-up waveform Ramp-up is applied to all scan electrodes Y at the same time. The ramp-up waveform Ramp-up causes a discharge to occur within cells of the entire screen. Wall charges of the positive polarity are accumulated on address electrodes X and sustain electrode Z and wall charges of the negative polarity are accumulated on scan electrodes Y, by means of the set-up discharge. In the set-down period SD, after the ramp-up waveform is applied, a ramp-down waveform Ramp-dn in which a voltage starts to drop from a positive voltage lower than a peak voltage of the ramp-up waveform to a ground voltage GND or a predetermined negative voltage level causes a weak discharge to occur within the cells. Some of the wall charges that are excessively formed is erased. Wall charges of the degree in which an address discharge can be generated stably by means of the set-down discharge remain within the cells in a uniform manner.
In the address period, a scan pulse scan of the negative polarity is sequentially supplied to the scan electrodes Y. At the same time, a data pulse data of the positive polarity is applied to the address electrodes X in synchronization with the scan pulse. While a voltage difference between the scan pulse and the data pulse and a wall voltage generated in the reset period are added, an address discharge is generated within cells to which the data pulse is applied. Wall charges of the degree in which a discharge can be generated are formed within cells selected by the address discharge when a sustain voltage is applied. A positive DC voltage Zdc is applied to the sustain electrode Z during the set-down period and the address period so that an erroneous discharge with the scan electrodes Y is not generated by reducing a voltage difference with the scan electrodes Y.
In the sustain period, a sustain pulse sus is alternately applied to the scan electrodes Y and the sustain electrode Z. While a wall voltage within the cell and the sustain pulse are added, a sustain discharge, i.e., a display discharge is generated between the scan electrodes Y and the sustain electrode Z in the cell selected by the address discharge whenever the sustain pulse is applied. Further, after the sustain discharge is completed, an erase ramp waveform Ramp-ers having a small pulse width and a low voltage level is supplied to the sustain electrode Z, thereby erasing wall charges remaining within the cells of the whole screen.
Meanwhile, the operation of the driving apparatus of the PDP in the address period and the sustain period will now be described in more detail with reference to FIG. 3.
FIG. 3 is a circuit diagram of a scan electrode (Y) driving unit and a sustain electrode (Z) driving unit that operate in the address period and the sustain period of the conventional PDP.
First, if a channel corresponding to a first scan electrode Y1 is selected in a scan process of the address period, channels corresponding to the remaining scan electrodes Y2, Y3, . . . , Yn are not selected.
If the channel is selected as such, a second switching element 113-1 of a first scan driver 110-1 corresponding to the selected channel is turned on, and a switching element 120 for scan is turned on.
At the same time, first switching elements 111-2 to 111-n of scan drivers 110-2 to 110-n corresponding to the channels that are not selected and a switching element 130 for ground are turned on.
If the switching elements operate and a data pulse is applied to the address electrodes X1 to Xm as such, a path from the address electrodes X to the scan electrodes Y corresponding to the selected channel, the second switch of the scan driver of the selected channel and a scan voltage source −Vyscan is formed. The current flows through the path. If such a path is formed, a write operation is performed on a cell located at a first line.
Furthermore, in a sustain process, a first switching element 140 for sustain, second switching elements 113-1 to 113-n of the scan drivers 110-1 to 110-n connected to the entire scan electrodes Y, and a switching element 160 for ground are turned on. Accordingly, a path from a sustain voltage source Vsy to the scan electrodes Y1 to Yn, the sustain electrodes Z1 to Zn and the switching element 160 for ground is formed. A high current flows through the path.
Further, a second switching element 150 for sustain, the first switching elements 111-1 to 111-n of the entire scan drivers 110-1 to 110-n and the switching element 130 for ground are turned on. Therefore, a path from a sustain voltage source Vsz to Z electrodes Z1 to Zn, the Y electrodes, the first switching elements 111-1 to 111-n of the scan driver, the switching element 130 for ground and the ground is formed. A high current flows through the path.
As described above, in the sustain process, the high current flows toward the scan electrode driving unit 100 and the sustain electrode driving unit 200 through the scan electrodes Y and the sustain electrodes Z, which are located on the left and right sides of the screen. Thus, noise is generated due to EMI (Electro Magnetic Interference). Further, since the electrode driving units are located at both sides, the construction of the circuit is complicated.
Moreover, in the case where the scan electrode driving unit 100 and the sustain electrode driving unit 200 are formed on one PCB (Printed Circuit Board), relatively lots of circuits are disposed on the left side because the sustain electrode driving unit 200 on the right side is disposed in the scan electrode driving unit 100 on the left side.
What the scan electrode driving unit 100 and the sustain electrode driving unit 200 are formed on one PCB as such also causes interference or noise to be generated between the electrode driving units because a high current flows between the scan electrode driving unit 100 and the sustain electrode driving unit 200, as described in FIG. 3. Further, there are many problems in that heat generated in each electrode driving unit affects other electrode driving units, etc.
In addition, if the scan electrode driving unit 100 and the sustain electrode driving unit 200 are disposed on a single PCB, the sustain electrodes and electrode pads on the right side have to be connected using a wire or other conductive material. Thus, impedance may vary due to the wire or other conductive material, and a voltage drop is generated. Accordingly, there are problems in that the brightness on the left side of a screen and the brightness on the right side thereof are different, and the like.